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1.
Summary 1. Kinetic studies showed that concurrent oxidation of preformed hydroperoxides may be expected to take place at all stages
of the autoxidation of methyl linoleate. The rate of oxidation relative to the rate of autoxidation of unoxidized ester is
determined chiefly by the extent of the accumulation of hydroperoxides.
2. Infrared spectral analysis of hydroperoxides oxidized to various degrees indicated that trans, trans diene conjugation and isolated trans double bonds produced in the autoxidation of methyl linoleate are related to the concurrent oxidation of the accumulated
hydroperoxides.
3. The low absorptivity observed for diene conjugation, compared to that which may be expected for the exclusive production
of cis, trans diene conjugated hydroperoxide isomers during the autoxidation of methyl linoleate is attributed to the concurrent oxidation
of accumulated hydroperoxides.
4. The effect of antioxidants in giving a well-defined induction period in the oxidation of hydroperoxides isolated from autoxidized
methyl linoleate indicated that the oxidation proceeds by a chain reaction.
5. The primary reaction products of the oxidation of hydroperoxides isolated from autoxidized methyl linoleate were found
to be polymers formed in a sequence of reaction involving the diene conjugation.
6. Studies on the autoxidation of methyl cis-9, trans-11-linoleate showed that cis, trans isomerization of the conjugated diene took place with the concurrent production of isolated trans double bonds and loss of diene conjugation.
Hormel Institute publication no. 138. Presented before the American Oil Chemists’ Society, Philadelphia, Pa., Oct. 10–12,
1955.
This work was supported by a grant from the Hormel Foundation. 相似文献
2.
Summary When autoxidized fatty esters and purified fatty hydroperoxides were decomposed in the absence of oxygen at 210°C., the principal
reaction was dimerization of the fatty acid chains with elimination of the hydroperoxide groups. Dimers isolated by molecular
distillation (60 to 90% of the polymer) have approximately 1 mole hydroxyl, 0.5 mole carbonyl, and two double bonds per mole
of dimer. Diene conjugation in the dimers from polyunsaturated fat hydroperoxides varied from 10 to 23%. The infrared spectra
of the dimers were similar to those of the original fatty esters except for one striking band at 2.9 μ, which is attributed
to the secondary hydroxyl group. The cis-trans diene in the polyunsaturated hydroperoxides was isomerized to the trans-trans configuration on dimerization. The methyl oleate hydroperoxide dimer showed only absorption for isolated trans double bond. The dimer was not split either by catalytic hydrogenation or by hydrogen iodide, indicating a carbon-carbon
bond between the monomer units. On oxidation with permanganate and periodate, the dimeric acids behaved like a monounsaturated
mixture containing double bonds in the C 6, C 7, C 8, C 9, and C 10 positions in the oleate dimer and in the C 8, C 9, and C 10 positions in the safflower ester dimer. Although the dimers showed no peroxidic oxygen iodometrically with potassium iodide,
a reduction occurred with hydriodic acid that may indicate the presence of intramolecular peroxide groups and/or allylic alcohol
or carbonyl groups. Bromination with N-bromosuc-cinimide and dehydrobromination with N,N-dimethyl aniline produced no aromatization.
Subsequent oxidation of the dehydrobrominated dimer yielded 2.6% residue, which was not aromatic. This evidence indicates
that the dimer does not have a six-membered cyclic structure. Dimerization of the hydroperoxides is suggested as occurring
through alkyl or alkoxy hydroperoxide radicals to give carbon-carbon linked fatty acid dimers and some higher polymeric units.
Presented at 33rd fall meeting, American Oil Chemists’ Society, Los Angeles, Calif., Sept. 28–30, 1959.
This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department
of Agriculture. 相似文献
3.
The reaction of mercaptoacetic acid with methyl linoleate and with linoleic acid was investigated. The reaction proceeded at low and erratic rates, with and without catalysts, such as peroxides at various temperatures, but could be accelerated by use of a large excess of mercaptoacetic acid. Addition of 1 mole of mercaptoacetic acid to 1 mole of methyl linoleate resulted in a product containing about 40% of mono-adduct. Ozonolysis of the purified mono-adduct yielded approximately equimolar quantities of caproic and azelaic acids, indicating that addition occurred about equally at the 9,10- and 12,13-ethylenic bonds. The dicarboxylic acid and the dimethyl ester of the mono-adduct and the tricarboxylic acid and trimethyl ester of the di-adduct of linoleic acid and mercaptoacetic acid were prepared, and the infrared spectra and some physical and chemical characteristics of these products were determined. The infrared spectra of the reaction products were obtained and correlated with functional groups which give rise to them. Bands at about 7.8 and 8.8 μ, commonly observed in long chain acids and esters and ascribed to C−O vibrations, are intensified in the sulfur-containing reaction products, suggesting characteristic absorption of C−S compounds at almost identical wavelengths. The formation of adducts was accompanied by a high degree of isomerization of the unreacted ethylenic bonds from the cis to the trans form both in the mono-adduct and in unreacted methyl linoleate. The methyl linoleate recovered contained about 12% diene conjugation, but catalytic quantities of mercaptoacetic acid were not effective in inducing conjugation. 相似文献
4.
- It has been confirmed that the principal products formed in the oxidation of methyl oleate by oxygen under a variety of conditions are predominantlytrans hydroperoxides. However no inversion of the double bond occurs in unoxidized oleate. Hence the conversion ofcis totrans double bonds and peroxide formation occur together in the same molecules.
- The autoxidation of methyl linoleate at low temperature yields predominantlycis,trans conjugated hydroperoxides. Autoxidation at 25°C., oxidation catalyzed by visible light, or ultraviolet light and copper soap catalyzed oxidation at temperatures appreciably above 0°C., lead to the formation primarily oftrans,trans conjugated hydroperoxides. The inversion of the second double bond in this case appears to be independent of the peroxide-forming reactions.
- The photochlorophyll oxidation of methyl linoleate leads to the formation of some unconjugated hydroperoxides, some of which containtrans double bonds.
- Under all of the conditions employed in the present investigation, the oxidation of methyl oleate and linoleate led primarily to the formation of monomeric peroxides which retained most of the unsaturation of the parent compound.
相似文献
5.
Geometrical isomers of methyl linoleate were reacted with alakli, and the resulting conjugated isomers were separated into trans,trans;cis,trans; and cis,cis fractions. The position of double bonds in the various fractions was determined by reductive ozonolysis. trans-9, trans-12-Isomer of linoleate formed trans,trans- and cis,trans-conjugated dienes, whereas cis-9, trans-12- and trans-9, cis-12-isomers in addition formed cis,cis-conjugated dienes. The formation of the products is in accordance with the theoretical predictions. During conjugation trans double bonds shifted to form a trans bond preferentially. During conjugation of cis-9, trans-12- and trans-9, cis-12-linoleate isomers, the cis double bond shifted preferentially over the trans double bond. A small amount of diene not conjugated was probably a geometrical and positional isomer of the starting material. 相似文献
6.
The effects of oxygen pressure, substrate concentration and solvent on the rate and products of oxidation of methyl linoleate
were studied at 50 C with azobisisobutyronitrile as a radical initiator. The absolute and quantitative numbers for oxygen
uptake, substrate disappearance, and formation of conjugated diene and hydroperoxides were measured. Under the present conditions,
4 conjugated diene hydroperoxides, 13-hydroperoxy-9- cis, 11- trans-( 2a), 13-hydroperoxy-9- trans, 11- trans-( 3a), 9-hydroperoxy-10- trans, 12- cis-( 4a), and 9-hydroperoxy-10- trans, 12- trans-( 5a) octadecadienoic acid methyl esters, were formed almost quantitatively. The rate of oxidation decreased with decreasing oxygen
pressure. However, the ratio of cis,trans to trans,trans hydroperoxides, ( 2a+4a)/( 3a+5a), was independent of oxygen pressure, and this ratio increased with increasing methyl linoleate concentration, as found recently
by Porter. Further, the rate of oxidation and the ratio of cis,trans/trans,trans hydroperoxides were dependent on solvent and increased with an increase in dielectric constant of solvent. A mechanism of
methyl linoleate oxidation consistent with these results is discussed.
Presented at the 15th Symposium on Oxidation Reactions, Nagoya, October 1981. 相似文献
7.
Summary A sample of debromination methyl linoleate has been autoxidized to a peroxide value of 671 m.e./kg. at approximately 0°C.
in the dark. An essentially pure concentrate of methyl octadecadienoate monohy-droperoxide was quantitatively separated; infrared
and ultraviolet spectral studies were made on the peroxide concentrate and on the corresponding hydroxyl derivative obtained
by reducing the peroxides with stannous chloride.
The infrared data showed no conjugated peroxides having geometric configurations other than cis, trans; the same data also
showed that the peroxide concentrate contained at least 90% conjugated cis,trans forms. Calculations based on ultraviolet
spectrophotometric methods also indicated that the peroxides were at least 90% conjugated. The remaining 10% of the sample
is most likely nonconjugated diene hydroperoxide. Since analogous cis, cis conjugated dienes have not been isolated and their
infrared and ultraviolet properties are unknown, their presence here in small amounts is possible. Ultraviolet and infrared
spectra of the reduced compounds conform closely to those of the peroxides except for reduction in the intensity of the OH
bond at 2.88 μ.
The infrared absorption spectra of the C−H structure and carbonyl groups of an essentially pure conjugated cis, trans methyl
octadecadienoate monohydroperoxide were recorded, using a LiF prism.
The infrared absorption spectra of the C−H strucfraction isolated from methyl linoleate autoxidized in the dark at 24°C. indicated
that appreciable amounts of conjugated trans, trans hydroperoxides were present, in addition to those of the cis, trans type.
It is possible that the conjugated cis, trans isomers were formed originally but were labile at the higher temperature and
in the presence of catalysts ( e.g., peroxides) were transformed to the thermodynamically more stable conjugated trans, trans isomer.
This work was supported in part by a contract between the Office of Naval Research, Department of the Navy, and the University
of Minnesota.
Hormel Institute publication No. 81, and paper No. 133, Journal Series, General Mills Research Laboratories. 相似文献
8.
α-Tocopherol and 1,4-cyclohexadiene were tested for their effect on the thermal decomposition of methyl linoleate hydroperoxide
isomers. The volatiles generated by thermolysis in the injector port of a gas chromatograph at 180°C were analyzed by capillary
gas chromatography. In the presence of either α-tocopherol or 1,4-cyclohexadiene, which are effective donors of hydrogen by
radical abstraction, volatile formation decreased in all tests, and significant shifts were observed in the relative distribution
of products in certain hydroperoxide samples. When an isomeric mixture of methyl linoleate hydroperoxides ( cis, trans and trans, trans 9- and 13-hydroperoxides) was decomposed by heat, the presence of α-tocopherol and 1,4-cyclohexadiene caused the relative
amounts of pentane and methyl octanoate to decrease and hexanal and methyl 9-oxononanoate to increase. A similar effect of
α-tocopherol was observed on the distribution of volatiles formed from a mixture of the trans,trans 9- and 13-hydroperoxides. This effect of α-tocopherol was, however, insignificant with pure cis,trans 13-hydroperoxide of methyl linoleate. The decrease in total volatiles with the hydrogen donor compounds, α-tocopherol and
1,4-cyclohexadiene, indicates a suppression of homolytic β-scission of the hydroperoxides, resulting in a change in relative
distribution of volatiles. The increase in hexanal and methyl 9-oxononanoate at the expense of pentane and methyl octanoate
in the presence of hydrogen donor compounds supports the presence of a heat-catalyzed heterolytic cleavage (also known as
Hock cleavage), which seems to mainly affect the trans,trans isomers of linoleate hydroperoxides. 相似文献
9.
The mixture of conjugated diene hydroperoxide isomers obtained from autoxidation of methyl linoleate was separated by high
performance liquid chromatography (HPLC). Four major isomers were obtained from adsorption chromatography and identified as
the 9 and 13 positional isomers having the trans-trans and cis-trans configurations. The latter geometrical isomers have the trans double bond adjacent to the hydroperoxide group. The hydroxy compounds (methyl hydroxylinoleates) obtained from the hydroperoxides
by NaBH 4 reduction were similarly separated but with improved resolution. This is the first instance of the complete separation of
these compounds and provides a rapid method for their analysis. Unlike adsorption chromatography, reversed-phase chromatography
separates the mixtures only according to the geometrical isomerism of the double bonds and not according to the position of
the hydroxy or hydroperoxide function. 相似文献
10.
The mechanism of hydrogenation at 900~950 psi with copper-chromite catalyst was investigated with pure methyl esters as well
as their mixtures. A comparison of double bond distribution in trans-monoenes formed during hydrogenation of linoleate and alkali-conjugated linoleate revealed that 85~95% of the double bonds
in linoleate conjugated prior to hydrogenation. The mode of hydrogen addition to conjugated triene and diene at high pressure
is similar to that at low pressure but positional and geometric isomerizations of unreduced conjugated esters were less at
high pressure. Geometric isomerization of methyl linoleate and linolenate was considerable at high pressure whereas it was
negligible at low pressure. The absence of conjugated products during hydrogenation of polyunsaturated fatty acid esters resulted
from their high reactivity. Conjugated dienes are 12 times more reactive than the triene, methyl linolenate, and 31 times
more reactive than the diene, methyl linoleate. The products of methyl linolenate hydrogenation were the same as those predicted
by the conjugation mechanism.
Presented at the 70th Annual Meeting of the American Oil Chemists' Society, San Francisco, April 29~May 3, 1979. 相似文献
11.
Determination of the relative reaction rates of isomeric methyl octadecadienoates is possible by competitive reduction of a mixture containing an inactive diene and a radioactively labeled isomer. The hydrogenation rate of methylcis-9,cis-12-octadecadienoate with platinum and nickel catalysts is compared to the hydrogenation rate of each of several isomers of methyl octadecadienoate, and the relative rate of the competitive hydrogenations is calculated by a digital computer. Methylcis-9,cis-12 linoleate is reduced the most rapidly of all the dienes studied. The relative rates of the positional isomers tend to decrease with the increasing number of methylene groups between the double bonds, except when one of the double bonds is in the more reactive 15 position. Comparison of the geometric isomers shows thattrans,trans diene is hydrogenated at a slower rate thancis,cis linoleate. 相似文献
12.
A high-performance liquid chromatographic method, using post-column detection with diphenyl-1-pyrenyl-phosphine (DPPP), was
developed for the quantitative and qualitative determination of isomeric lipid hydroperoxides (OOH). The OOH eluted from a
normal-phase column were passed through a photodiode array detector and then mixed with DPPP solution in a reaction coil heated
at 80°C. DPPP oxide formed by the reaction with OOH was determined by monitoring the fluorescence intensity at 380 nm and
excitation at 352 nm. The conjugated diene OOH (13- cis, trans- and 9- cis, trans-OOH) and nonconjugated OOH (12- cis-trans- and 10- cis, trans-OOH) from photosensitized oxidation of methyl linoleate were determined in a molar ratio of 31∶29∶19∶21, respectively. However,
only the two conjugated hydroperoxides were detected by ultraviolet absorption at 234 nm. Further applications were carried
out for the determination of OOH of methyl oleate and methyl linolenate. This method proved to be useful for the determination
of the OOH containing both conjugated and nonconjugated diene structures. 相似文献
13.
A liquid partition chromatographic method was developed to isolated and determine hydroperoxides in autoxidized fatty acids
or their methyl esters. By the use of benzene containing 2 to 4% methanol as the mobile solvent, the hydroperoxides were separated
from unoxidized fatty acids or methyl esters and from secondary and polymeric decomposition products. In the analyses of oxidized
fatty acids, diethyl ether was necessary to elute the secondary decomposition products.
Saponification of autoxidized fatty esters destroyed the peroxides as determined iodometrically, but the resulting acids contained
a fraction which was eluted in the same position as hydroperoxide acids. Evidence showed that this fraction is a monomeric
hydroxy fatty acid containing conjugated cis-traux and trans-trans unsaturation.
Fatty ester hydroperoxides were isolated chromatographically in yields and purity comparable to those reported in the literature
by countercurrent distribution. The concentrations of methyl linoleate hydroperoxide determined chromatographically were smaller
than indicated by the peroxide value and diene conjugation of the autoxidized methyl linoleate.
This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department
of Agriculture. 相似文献
14.
Summary The rates of polymerization of alpha and beta eleostearates agree with second order kinetics, as would be expected for a bimolecular
Diels-Alder addition. The all- trans, beta isomer reacts faster than the cis, trans, trans alpha isomer, in agreement with known cis, trans effects on diene activity.
The polymerization of normal linoleate follows an apparent first order reaction. It is suggested that conjugation is the slow
rate determining monomolecular reaction, as has been proposed for the non-conjugated linoleate isomers.
Paper No. 177, Journal Series, Research Laboratories, General Mills Inc. Presented at the 28th fall (Paul Bunyan) meeting
of the American Oil Chemists’' Society, Oct. 12, 1954, Minneapolis, Minn. 相似文献
15.
In order to study antioxidant action on lipid hydroperoxide decomposition, the effects of α-tocopherol (TOH) and ascorbyl
palmitate on the decomposition rate and reaction sequences of 9- and 13- cis,trans methyl linoleate hydroperoxide ( cis,trans ML-OOH) decomposition in hexadecane were studied at 40°C. Decomposition of cis,trans ML-OOH as well as the formation and isomeric configuration of methyl linoleate hydroxy and ketodiene compounds were followed
by high-performance liquid chromatographic analysis. TOH effectively inhibited the decomposition of ML-OOH. The decomposition
rate was two times slower at 0.2 mM and more than 10 times slower at 2 and 20 mM of TOH. Ascorbyl palmitale (0.2, 2, and 20
mM) slightly accelerated the decomposition of ML-OOH. Both compounds had an effect on the reaction sequences of ML-OOH decomposition.
At high levels TOH inhibited the isomerization of cis,trans ML-OOH to trans,trans ML-OOH through peroxyl radicals and increased the formation of hydroxy compounds. Further, the majority of the hydroxy and
ketodiene compounds formed had a cis,trans configuration, indicating that cis,trans ML-OOH decomposed through alkoxyl radicals without isomerization. These results suggest that when inhibiting the decomposition
of hydroperoxides, TOH can act as a hydrogen atom donor to both peroxyl and alkoxyl radicals. In the presence of ascorbyl
palmitate, cis,trans ML-OOH decomposed rapidly but without isomerization. In contrast to TOH, the majority of hydroxy compounds were cis,trans, but the ketodiene compounds were trans,trans isomers. This indicates that ascorbyl palmitate reduced cis,trans ML-OOH to the corresponding hydroxy compounds. However, the simultaneous formation of trans,trans ketodiene compounds suggests that ML-OOH decomposition, similar to the control sample, also occurred in these samples. Thus,
under these experimental conditions, the reduction of ML-OOH to more stable hydroxy compounds did not occur to an extent significant
enough to inhibit the radical chain reactions of ML-OOH decomposition. 相似文献
16.
Various arene-Cr (CO) 3 complexes and Cr(CO) 6 are effective soluble catalysts for the conjugation of polyunsaturated fats. Methyl benzoate-Cr(CO) 3 is one of the most active catalysts. The following conjugation levels were obtained: methyl linoleate, 65%; methyl linolenate,
45%; the polyunsaturates in soybean and safflower oils, 73%; and in linseed oil 48%. Conjugated dienes from linoleate were
predominantly cis,trans in configuration. Their double bonds were distributed between C 5 and C 16 of the fatty acid chain. Hydrogenation and dehydrogenation are side reactions, which seem to limit the yield of conjugated
dienes from methyl linoleate. A conjugation mechanism is proposed that involves allyl-HCr(CO) 3 complexes as intermediates undergoing 1,3- and 1,5-hydrogen shifts.
Presented at the AOCS Meeting, San Francisco, April 1969.
No, Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
17.
Methyl linolenate hydrogenated at 140°C, with 0.5% Ni catalyst and 1.1 mole of hydrogen at atmospheric pressure was separated
into octadecenoate, octadecadienoate, and octadecatrienoate fractions by countercurrent distribution. Gas chromatography on
a 200-ft. capillary Apiezon L column revealed one component in the triene fraction, four in the diene fraction, and nine in
the monoene fraction. These components were partially fractionated by low-temperature crystallization, and their solubilities
were correlated with alkali conjugation results, with infrared data for cis and trans configuration of bonds and with dibasic acids isolated from the fractions after oxidative cleavage. Approximately 45% of trans acids were present in both the monoene and diene fractions. Considerable migration of double bonds from the original 9, 12,
and 15 positions occurred. Cis,cis dienes which could not be conjugated by alkali were formed. Little alteration of the residual methyl linolenate was observed.
The results demonstrate the applicability and utility of new techniques of fractionation and analysis to the study of the
hydrogenation mechanism.
Presented at 51st annual meeting, American Oil Chemists' Society, Dallas, Tex., April 4–6, 1960.
This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department
of Agriculture. 相似文献
18.
Soybean oil was partially hydrogenated with copper-chromite catalyst at 170 C and up to 30,000 psig hydrogen pressure. Catalyst
activity increased with increase in pressure up to 15,000 psig. The linolenate selectivity (S Ln) of the reaction remained essentially unchanged over 50–1000 psig pressure range. A S Ln of 5.5 to 5.6 was achieved at 15,000 to 30,000 psig pressure range. This value is somewhat lower than the selectivity at
50–1000 psig, but much higher than that obtained with nickel catalysts. Geometric isomerization increased as pressure increased
up to 200 psig; above this pressure, the percent trans remained the same up to 500 psig. trans Isomer content decreased when the pressure was increased to 30,000 psig. cis, trans Isomerization of linoleate was greater at 1000 psig and 15,000 psig than at 50 psig. At 15,000 psig, part of the linoleate
in soybean oil was hydrogenated directly without prior conjugation, whereas at low pressures, all of the double bonds first
conjugate prior to hydrogenation. This difference in mechanism might explain the lower selectivities obtained at high pressures.
Conjugated diene isomers were found in the products up to 200 psig. Above this pressure conjugated diene was not measurable.
No significant differences were found in the double bond distribution of trans monoenes even though the amount of trans monoene formed decreased as pressure was increased to 30,000 psig.
1 Presented at the AOCS meeting, San Francisco, May 1979. 相似文献
19.
The prooxidant property of inorganic chromium compounds was determined in methyl linoleate free from natural antioxidants
and metals. Prooxidant properties of inorganic chromium compounds appeared in order of sodium chromate > chromium (VI)-oxide
> chromium chloride > potassium chromate > chromium (III)-oxide > potassium dichomate. In comparison with the control, additions
of chromium compounds induced different amounts of autoxidation products derived from methyl linoleate, such as small amounts
of hydroperoxides and conjugated dienes and large amounts of hydroxy groups, α,β,γ,δ-unsaturated carbonyls, isolated trans double bonds, polymers, and free radicals. From these analytical data, the catalysis of chromium compounds in the autoxidation
of methyl linoleate seemed to be based on their abilities of abstracting a hydrogen from methyl linoleate and decomposing
hydroperoxides derived from the autoxidation of methyl linoleate. 相似文献
20.
The accumulation of peroxides, carbonyl com-pounds and reducing substances during irradia-tion and post-irradiation storage
of pure fatty acid methyl esters has been studied.
Irradiation and storage of irradiated methyl myristate under vacuum results in formation of small quantities of these compounds.
Irradiation under oxygen gives peroxides and carbonyl com-pounds in yields indicating that every ionization results in the
formation of one molecule of each group, and antioxidants have no effect on the formation of these compounds during irradiation.
Irradiation of methyl linoleate under vacuum results in destruction of pre-formed hydroperox-ides. During irradiation in oxygen,
approximately one-eighth of the peroxides formed arises from the direct reaction of irradiation-induced free radi-cals with
oxygen, while the rest is formed through a chain mechanism with an average chain length of 7.
Peroxides continue to accumulate in irradiated methyl linoleate stored under oxygen at a rate increasing with initial irradiation
dose.
Antioxidants have some effect in retarding the formation of peroxides during irradiation of methyl linoleate and during post-irradiation
stor-age, but the effect is small compared to their antioxygenic activity toward simple autoxidation. The effect varies with
the nature of the antioxi-dant and with irradiation dose. Propyl gallate is much less effective than butylated hydroxy-anisole
and appears to be easily destroyed during irradiation.
For paper I of this series, see Ind. Eng. Chem. 49. 1713 (1957).
Presented at the AOCS Meeting in Minneapolis, 1963. 相似文献
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